Semiconductor devices, such as those used for microprocessors, are typically fabricated by bonding silicon dioxide layers on a silicon substrate. The silicon dioxide layers are selectively etched away with a plasma current to expose the silicon substrate. Exposed silicon on either side of a non-etched area is typically implanted with ions to create source and drain areas. The conductive layer is then deposited on the nonexposed area to create a gate for the transistors. Additional conductive layers are then typically disposed on the source and drain areas to provide electrical connection thereto. The conductive layers are separated by a dielectric material and multiple layers of conductive material are also disposed elsewhere on the substrate to provide pads for external connection to the devices.
A particular set of steps utilized in the fabrication of semiconductor devices include a first implant step, the deposition of a layer of oxide, and a second implant step.
In a conventional method, the oxide layer is grown by utilizing a high temperature, such as a temperature approximating 900.degree. C., and using oxygen gas to grow a thin oxide layer, such as a thickness of approximately 100 Angstroms. A problem with using this conventional method is that the high temperature required tends to drive the first implant material too far into the silicon substrate. This unwanted thermal driving of the implant material can cause semiconductor devices to be unsuitable for sophisticated, high performance use.
One method which addresses the problems caused by the required use of such a high temperature is a method utilizing plasma enhanced chemical vapor deposition (PECVD). This alternative method is commonly referred to as Novellus Concept 1. The Novellus Concept 1 allows the use of a low temperature, such as approximately 400.degree. C., thus addressing the problem of driving the first implant material too far into the silicon substrate.
However, when the temperature is reduced from a high temperature such as 900.degree. C. to a low temperature such as 400.degree. C., the very thin oxide film property becomes very porous and tends to be very poor quality, thus allowing too much implant material to flow through the oxide layer. Additionally, it is highly difficult to control each deposition station such that only the minuscule required amount of oxide is deposited. For example, if five stations are used in the deposition chamber, and an oxide thickness of 100 Angstroms is desired, each station would need to contribute only 20 Angstroms to the oxide thickness. This kind of fine control would be extremely difficult. Consequently, the oxide layer resulting from the Novellus Concept 1 is typically very thick, such as approximately 500 Angstroms.
A problem with such a thick oxide layer is that not enough of the implant material can penetrate through the oxide layer.
What is needed is a method and system for providing an oxide layer for a semiconductor device during fabrication which utilizes a relatively low temperature and produces a very thin oxide layer which has properties sufficient to properly perform its function of allowing an acceptable amount of implant material to penetrate through it. The present invention addresses such a need.